Recent advances in medical imaging technology have introduced functional magnetic resonance imaging (fMRI), which is capable of acquiring sequences of images of brain activity by measuring changes in blood oxygenation levels. Functional magnetic resonance imaging is increasingly used in the medical field to scan subjects, both normal and diseased. The fMRI data is a 4-dimensional dataset involving 3 spatial dimensions and one temporal dimension. fMRI has been used to study the function of brain. fMRI can give high quality visualization of location of activity within the brain, allowing for a comparison of the functions of control and disordered brains.
Brain activity can be analyzed using fMRI to diagnose disorders. For example, Attention Deficit Hyperactivity Disorder (ADHD) is one of the most commonly found behavioral disorders among children. Almost 3-5% of school aged children are diagnosed with ADHD. At present, no well-known biological measure exists to diagnose ADHD. Instead, people rely on the behavioral symptoms to identify the disorder. To understand the cause of the disorder more fundamentally, researchers are using new structural and functional imaging tools, such as fMRI.
fMRI has been used to study and diagnose different functional disorders of brain. In some analyses, task-related fMRI data is used where the test subjects perform some conscious tasks depending on the input stimuli. On the other hand, some studies use resting state brain fMRI data. Even when the brain is in the resting state, a network region, known as the default mode network (DMN) of the brain, remains active. It is believed that the DMN may be responsible for synchronizing all parts of the brain's activity; and disruptions to the network may cause a number of complex brain disorders.
Researchers have studied neural substrates relevant to ADHD related behaviors such as attention lapses, and associated the DMN as a key area for observation for a better understanding of the problem. Studies have been proposed to identify ADHD related defects. Some of the studies use group label analysis to deduce statistical differences between ADHD conditioned and control groups. Structural MRI analysis has suggested that there are abnormalities in ADHD brains, specifically in the brain areas such as frontal lobes, basal ganglia, parietal lobe, occipital lobe and cerebellum. In another set of studies, ADHD brains were analyzed using task-related fMRI data. Significantly low activity was found in the anterior cingulated cortex when ADHD subjects were asked to perform the CountingStroop during fMRI. It has also been shown that ADHD conditioned children have difficulties in performing go/nogo task and have decreased activity in frontostriatal regions, and that boys with ADHD have higher T2 relaxation time in the putamen, which is directly connected to a child's capacity to sit still.
Other work has been performed using the resting state brain fMRI to find out the abnormalities in the DMN if any. A Generalized Linear Model based regression analysis has been performed on the whole brain with respect to three frontal foci of the DMN and, which found low negative correlated activity in the precuneus/anterior cingulated cortex in ADHD subjects. Among other studies, functional abnormalities were found in the dorsal anterior cingulated cortex, and decreased regional homogeneity was shown in the frontal-striatal-cerebellar circuits, while increased regional homogeneity was shown in the occipital cortex among boys with ADHD. Decreased Amplitude of Low-frequency fluctuation (ALFF) in the right inferior frontal cortex, left sensorimotor cortex, bilateral cerebellum and the vermis was shown, as well as increased ALFF in the right anterior cingulated cortex, left sensorimotor cortex and bilateral brainstem.
While group level analysis can suggest statistical differences among two groups, it may not be useful for clinical diagnosis on an individual level. Accordingly, there is a need for methods and systems which can be used to diagnose and classify disorders, such as ADHD, on an individual level, which can connect synchronous regions of a brain.